Pultrusion apparatus

ABSTRACT

A method for producing a pultrusion product having a variable cross-section using a specially adapted temperature controllable pultrusion die includes the steps of pulling reinforcing fibers which have been impregnated with a heat curable thermosetting polymeric resin composition through a temperature controllable die, heating the temperature controllable die to a temperature sufficient to effect curing of the thermosetting resin, cooling the temperature controllable die to a temperature which is sufficiently low to prevent any significant curing of thermosetting resin passing through the pultrusion die, pulling the cured material and a predetermined length of uncured material from the die, reshaping the uncured material, and curing the reshaped material. The reshaping step can be used to provide off-sets, flanges, bosses and the like. The method and associated apparatus of the invention provide a relatively simple and inexpensive way of producing fiber-reinforced thermoset plastics having a variable cross-section.

CROSS-REFERENCE

This application is a division of U.S. Ser. No. 08/370,798, filed Jan.10, 1995, now U.S. Pat. No. 5,556,496 of Joseph E. Sumerak, for"PULTRUSION METHOD FOR MAKING VARIABLE CROSS-SECTION THERMOSETARTICLES".

FIELD OF THE INVENTION

This invention relates to the preparation of fiber-reinforced thermosetarticles, and more particularly to a pultrusion process and apparatusspecially adapted for producing pultruded thermoset articles having avariable cross-section with respect to the longitudinal axis or machinedirection of the pultruded article.

BACKGROUND OF THE INVENTION

Pultrusion has become recognized as one of the most efficient methodsavailable for manufacturing fiber-reinforced engineered compositematerials, especially thermoset composites. Pultruded products areespecially noted for their high fiber volume content relative toproducts made by alternative manufacturing processes, making themparticularly strong materials which are preferred in many structuralapplications. Commercial processes for producing pultruded thermosetarticles have been generally limited to the production of productshaving a constant cross-section with respect to the longitudinal axis ormachine direction. Thermoplastic pultrusion technology does allow forlimited geometry reshaping after primary molding, however, the cost ofraw materials and processing steps is severely cost prohibitive for mostapplications. Pultrusion techniques which allow for the production ofthermoset articles having a variable cross-section are desirable inorder to introduce, for example, flanges, off-sets, bosses, and the likewhich can provide secondary structure for improved load transfer andjoint efficiency.

SUMMARY OF THE INVENTION

The present invention provides an improved process for producingthermoset pultruded articles having a variable cross-sectional profile,and overcomes various disadvantages of the prior art. In particular, theprocess provides a practical and relatively inexpensive method forproducing pultruded articles of variable cross-section by varying thetemperature within the pultrusion die as a thermosetting resinimpregnated fiber mass is pulled through the pultrusion die to provide acontinuous pultruded article having at least one portion which issubstantially fully cured and at least one other portion which issubstantially uncured. The uncured portion is subsequently reshaped andcured to form a pultruded article having a variable cross-section. Theinvention provides a simpler, more cost effective process forcontinuously producing pultruded articles of variable cross-sectionwhich have relatively uniform fiber content and high strengthcharacteristics. The process can also be used for integrally placingregistration marks, raised letters or other insignia on the article.Furthermore, localized cross-sectional shape change can provideopportunities to selectively introduce more efficient load transfer orfastening geometries along the length of a pultruded profile.Additionally, the process is well suited to a variety of commercialapplications.

The process comprises the steps of pulling a reinforcing materialimpregnated with a heat curable thermosetting polymeric compositionthrough a temperature controllable pultrusion die, controlling thetemperature of the pultrusion die and the drawing speed of the materialso that a predetermined length of material in the pultrusion die will besubstantially cured, rapidly lowering the temperature of the pultrusiondie so that a predetermined length of the material passing through thepultrusion die will remain substantially uncured, reshaping the uncuredportion of the material emerging from the pultrusion die, and curing thereshaped portion. Optionally, before the uncured portion of materialemerging from the pultrusion die is reshaped and cured, material such asadditional resin, fiber, resin impregnated fiber mass such as sheetmolding compound (SMC) or bulk molding compound (BMC), metallic inserts,etc. can be added to the uncured portion and will become an integralpart thereof after the reshaping and curing steps.

The uncured portions are preferably reshaped and cured immediatelydownstream of the pultrusion die before the pultrusion product is cutinto individual articles. Alternatively, the product emerging from thepultrusion die can be cut as desired and the uncured portions can bereshaped and cured in a separate operation.

The invention is also drawn to an apparatus for forming afiber-reinforced thermoset article having a variable cross-section,which includes means for drawing or pulling a thermosetting resinimpregnating fiber mass through a die having heating means for rapidlyraising the temperature of the die to effect curing and cooling meansfor rapidly lowering the temperature below that needed to effect curing,thereby allowing preparation of a continuous article having asubstantially fully cured portion and a substantially uncured portionwhich can be reshaped and cured to form a fiber-reinforced articlehaving a variable cross-section or profile. The apparatus differs fromconventional pultrusion apparatus in that it is capable of controllingthe level of cure at the die exit through rapid manipulation of thepultrusion die temperatures. Thus the die can be heated to causesubstantial cure of thermosetting resins passing therethrough andsubsequently rapidly cooled to a temperature wherein the thermosettingresin of another longitudinally aligned portion of the material passingthrough the die will remain substantially uncured. The apparatus furtherdiffers from conventional pultrusion apparatus in that the control oftemperatures and process speed are designed for unsteady stateprocessing rather than steady state processing and must be fullyvariable at any instant of time to execute variations in temperature andspeed which make the process possible.

To facilitate rapid heating and rapid cooling of the die, therebyallowing commercially reasonable cycling times and production rates, themass of the die is necessarily considerably less than that ofconventional dies. More specifically, the dies preferably haverelatively thin walls as compared with conventional dies, with the outerwalls of the die generally conforming to the shape of the die cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an apparatus for carrying out themethod of the present invention;

FIG. 2 is a cross-sectional elevation of the pultrusion die of theinvention transverse to the machine direction of the apparatus;

FIG. 2a is cross-sectional elevation of a pultrusion die having aheating/cooling jacket;

FIG. 2b is a cross-sectional elevation of a single piece pultrusion die;

FIG. 2c is a cross-sectional elevation of a pultrusion die for formingan article having a H-shape cross-section;

FIG. 3 is a longitudinal cross-section of a reshaping die which can beused with the process of the invention;

FIGS. 4 and 4a are schematic illustrations of a gripper/puller andassociated means for detecting a cross-sectional change in the geometryof pultruded material to prevent the gripper/puller from clamping ontoand damaging the reshaped portion of the pultruded product;

FIGS. 5 and 5a are longitudinal cross-sections of a reshaping die havingmeans for piercing and selectively shearing fibers of pultruded materialduring reshaping of uncured portions thereof;

FIG. 6 is a longitudinal cross-section of a pultruded product which hasbeen pierced and reshaped using the reshaping die shown in FIGS. 5 and5a;

FIG. 6a is a perspective view of the product shown in FIG. 6;

FIG. 7 is a perspective view of a pultruded rod with an end portionwhich transitions from a circular to an oval cross-section;

FIG. 8 is a perspective view of a pultruded tubular product having areshaped reduced outer cross-sectional perimeter at one end whichconforms to the inner perimeter of the remaining portions of theproduct;

FIG. 9 is a perspective view of a pultruded tubular product having atapered end; and

FIG. 10 is a perspective view of a pultruded product having arectangular tube to an I-shaped cross-sectional transformation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pultrusion die used in the practice of the invention is generallysimilar to conventional pultrusion dies except that it is speciallydesigned to facilitate rapid thermal cycling. In particular, thepultrusion die is provided with heating means such as electricalresistance heaters or a liquid or gaseous heat transfer fluid which canbe circulated through or around the outer surfaces of the pultrusion dieto rapidly raise the temperature of at least a portion of the pultrusiondie above the temperature needed to effect curing of the heat curablethermosetting polymeric material, and cooling means such as a liquid orgaseous heat transfer fluid which can be circulated through or aroundthe outer surfaces of the pultrusion die to rapidly lower thetemperature of the pultrusion die below that temperature whereinappreciable curing of the heat curable thermosetting polymeric materialcan occur. Preferably the heating and cooling means each extendsubstantially the entire length of the die along the direction throughwhich the pultruded material is drawn so that the temperature ofsubstantially the entire die can be raised above that needed to causecuring of the thermosetting resin and lowered to a temperaturesufficiently low to inhibit curing of the thermosetting resin. The wallthickness of the pultrusion die is preferably relatively thin ascompared with conventional pultrusion dies to reduce the amount of heattransfer needed to achieve a desired temperature change of thepultrusion die. More specifically, the wall thicknesses of thepultrusion die are minimum in order to reduce thermal mass and yetprovide the mechanical optimized properties necessary to withstand theforces which arise within the pultrusion die due to the frictionalresistances and thermal expansion of the liquid, gel and solid regionsof the material passing along the internal walls of the pultrusion die.

The invention allows production of pultruded articles of generally anydesired length of constant cross-section having a localized variablecross-section shape introduced at any axial location along the productlength and having uniform high fiber content and uniform fiber to resinbonding characteristics throughout. By contrast, known processes forproducing variable cross-section pultruded products have generallyinvolved the use of steady state pultrusion curing techniques utilizingone or a plurality of identical heated variable cross-section dies whichclose upon a moving stream of resin impregnated fiberous material towhich additional thermosetting material may be added. The heated die ordies remain closed as the material cures while moving downstream. Whenthe material has cured the die is opened and returned or cycled backupstream in the process. The articles produced by these known processesgenerally have an identical cross-sectional repeat sequence defined bythe length of the molding die or dies along the length of the continuousprocess stream. An example of such a process is hammer handle blankswhich are of relatively short length. Other proposed methods forproducing pultruded products having a variable cross-section shape andrelatively uniform fiber content and uniform fiber to matrix bondinghave not yet been proven to be successful and/or have been limited topolymerizable compositions capable of achieving a B-staged low level ofcure, such as epoxy resins, which require storage of material at reducedtemperatures until subsequent reshaping and cure is undertaken.

An embodiment of the invention will now be described with respect to apultrusion apparatus for pultruding a sheet or strip having a generallyrectangular shape cross-section. It should be understood, however, thatthe invention is applicable to molding of articles having generally anydesired shape, including tubes and rods having square, circular,rectangular trapezoidal, X-shaped, T-shaped, J-shaped, I-shaped or otherregular or irregular cross-sectional shape or profile. Cross-sectionalshape or profile as used herein, unless otherwise noted, refers to theshape of the pultruded article in a cross-section which is viewed alonga line coincident or parallel with the direction from which thepultruded article emerges from the pultrusion die, i.e. the shape of across-section which is perpendicular with the machine direction.

Referring to FIG. 1, a pultrusion apparatus is generally designated bythe numeral 10. The apparatus includes a plurality of creels or spools12 from which reinforcing fibers 13 are supplied and drawn through guide14 which guides and converges the reinforcing fibers which are pulledthrough resin bath 16. The reinforcing fibers 13 are passed aroundseveral redirect bars 18 which cause spreading of the fibers in the bathand provide for thorough impregnation of each of the fibers with aliquid heat curable thermosetting resin contained within the resin bath16. Various alternative techniques which are well known to the art canbe employed to apply or impregnate the fibers 13 with thermosettingresin. Such techniques include, but are not limited to, spraying,dipping, roll coating, brushing and the like. Alternatively,preimpregnated fibers can also be used. Other known techniques which canbe employed to impregnate the fibers with thermosetting resin includepressure assisted impregnation which is also often referred to as resininjection. The resin impregnated reinforcing fibers 19 emerging fromresin bath 16 are pulled through a forming guide system 20 which, forexample, can be comprised of one or a plurality of machined plates,sheet metal guides or like, which consolidates the resin impregnatedfibers 19 into the approximate shape of the desired pultruded article.The consolidated mass of resin impregnated fibers 22 emerging from theforming guide system 20 is pulled through a temperature controllablepultrusion die 26 which is capable of undergoing rapid temperaturecycling and passes to a gripping/pulling means 28. Heating means 23 andcooling means 24 are provided to selectively heat and cool the die 26 asrequired so that a first portion (i.e. length) of the material 27emerging from the die is substantially fully cured and a secondlongitudinally aligned portion (i.e. length) is substantially uncured.It should be understood that the heating means 23 and cooling means 24are preferably comprised of a plurality of individually controllableheating and cooling means respectively to facilitate optimal temperaturecontrol along the entire length of the die (for example, to achieve anoptimal cure profile and to subsequently cool it). The substantiallyuncured portion of the material emerging from die 26 is reshaped andcured by reshaping die 32. After passing through the pulling means 28,the composite 24 is cut into articles of desired length by a cuttingmeans 30 which can be generally any known means suitable for cuttingthermoset articles such as a circular saw, band saw or the like.

Conventional pultrusion processes are generally operated at steady stateconditions, i.e. temperature and other process parameters generallyremain relatively constant at any location in the process stream. Thepresent invention involves an unsteady state process wherein thetemperature in the pultrusion die 26 alternates between temperatures ator above the temperature needed to effect polymerization reactions andcuring of the heat curable thermosetting polymeric resin, andtemperatures which are sufficiently low to prevent or retard anysignificant reaction or curing of the heat curable thermosetting resincomposition.

A cross-sectional elevation transverse to the machine direction (i.e.the direction that the thermosetting resin impregnated fiberous mass ismoving) of the temperature controllable pultrusion die is shown in FIG.2. The pultrusion die 26 includes an upper die part 34 and a lower diepart 36 having recessed areas 38 and 40 respectively which togetherdefine a die cavity 42. The upper die part 34 and lower die part 36 arepreferably held together such as by socket head cap screws 43 which passthrough upper die part 34 and are secured to lower die part 36 through acorresponding threaded bore 44 in lower die part 36, although othermeans such as clamps can be used to hold the die parts together.Alternatively, a die 26b (shown in FIG. 2b) having a single piececonstruction with a predefined closed cavity can be employed, such asseamless tube dies or dies produced using the wire EDM process, whicheliminate the need for fasteners. The pultrusion die includes heatingmeans such as an electrical heater resistance strip 46. Alternatively,other conventional heating means can be provided such as external platenheaters, infrared heaters, cartridge heaters, quartz heaters, conduitsor channels provided in the die parts for circulating a heated fluid,and the like. Sufficient heating means 46 are provided so that thetemperature of substantially the entire pultrusion die 26 can be rapidlyheated to a desired axial temperature profile suitable for continuoussteady state pultrusion processing.

Conventional pultrusion dies are provided with heating means formaintaining a heating zone at a relatively constant temperaturesufficient to effect curing of the thermosetting resin passing throughthe die cavity, but are not provided with cooling means for lowering thetemperature within the heating zone below that necessary to effectcuring, although conventional pultrusion dies often which include acooling zone with associated cooling means at the entrance of the die toavoid curing in the tapered or radiused entrance region. Cooling meansmay be included at the exit end of the die to suppress the temperatureof the already cured material to avoid thermal stress cracking which mayoccur as the hot material exits the die.

By contrast, the pultrusion die 26 of the present invention alsoincludes cooling means capable of rapidly absorbing heat from thepultrusion die 26 so that the temperature at the mold cavity surfaces 38and 40 can be rapidly lowered ,e.g. less than 3 minutes and desirablyless than 1 minute, to a temperature below that wherein appreciablecuring of the heat curable thermosetting resin can occur. Unlikeconventional pultrusion dies which are either devoid of cooling means orinclude cooling means only at localized cooling zones at the entranceand/or exit of the die, the pultrusion die of the present invention isprovided with heating and cooling means capable of achieving rapidthermal cycling so as to abstract heat from heated die areas which couldotherwise initiate cure. Suitable cooling means include any conventionalmeans known to the art for directly or indirectly cooling the die. Suchcooling means include fans, blowers, or the like for moving cool air orother cool gases past the outer surfaces of the pultrusion die to effectrapid convective cooling. Another suitable means for rapidly cooling thepultrusion die is with cooling coils which are embedded within orotherwise in thermally conductive contact with the pultrusion die, andthrough which a cool fluid is circulated. As another alternative, thepultrusion die 26 can be provided with a combination heating/coolingjacket 70 which completely surrounds the pultrusion die, as shown inFIG. 2a. The inner walls 72 of the jacket 70 are spaced from the outerwalls 74 of the pultrusion die to provide a space 76 therebetweenthrough which cooling and heating fluids can be alternately circulatedto cool and heat the pultrusion die 26 as desired. A plurality ofthermocouples 77 can be provided at selected locations within thepultrusion die 26 as desired for automated temperature control.

In order to facilitate rapid thermal cycling of the temperaturecontrollable pultrusion die 26, the pultrusion die parts 34 and 36preferably have relatively thin walls to reduce the amount of heat whichmust be added or removed by the heating and cooling means respectivelyin order to achieve the temperature changes required to effect andprevent curing of the thermosetting resin respectively. Of course, themechanical and thermal properties of the die material will effect thethermal mass. As an example, copper base tooling alloys can be used forthe die as compared to P20 grade tool steel. Suitable wall thicknesses,i.e. the shortest distances between the internal walls 38 and 40 and theexternal walls 74 of the pultrusion die, are desirably less than 1/2inch and preferably less than or about 1/4 inch. Most preferably thewall thicknesses of the pultrusion die parts are the minimum wallthickness required to provide the structural strength necessary toconstrain forces imposed upon the die by the material passingtherethrough. More specifically the thickness of the pultrusion diewalls is preferably about the minimum needed to limit deformation of thedie wall to a tolerable level which will not interfere with successfulprocessing of the material passing through the pultrusion die. Asuitable die wall thickness is generally one wherein the cavitydeformation does not exceed 0.002 inches when subjected to internalpressures which are typically imposed on the pultrusion die. Internalpressures imposed in the pultrusion die can generally range from about50 to 500 psi, and more typically up to about 200 psi. Suitable wallthicknesses can be determined experimentally, but are more preferablyestimated using mathematical modeling techniques such as finite elementanalysis. It has been determined that the mass of the pultrusion die cangenerally be reduced to about 10 to about 20 percent of the mass ofconventional pultrusion dies which are not subjected to rapidtemperature cycling. The length of the pultrusion die is generally fromabout 12 to 96 inches, and more typically from about 30 to about 60inches. In order to achieve a low mass die which can be easily heated toa temperature which will cure thermosetting resin passing therethroughand easily cooled to temperatures below that where curing occurs, thecross-sectional shape of the outer walls most generally conform to theshape of the die cavity so that the thickness of the die walls aregenerally less than about 1/4 around the entire cross-sectionalperimeter. For example, in accordance with the principles of theinvention, in order to reduce die mass and permit rapid temperaturecycling of the die, the outer cross-sectional perimeter of a die 78having a die cavity 79 with an H-shaped cross-section would also have asubstantially conforming H-shape such as shown in FIG. 2c. This differssubstantially from conventional pultrusion dies which are generallymassive to provide for better thermal stability and wherein the outercross-sectional perimeter of the die is generally rectangular regardlessof the shape of the die cavity.

The pultrusion apparatus of the invention preferably includes areshaping die 32 which is positioned immediately downstream of thetemperature controllable pultrusion die 26. A matched metal mold (i.e.compression mold) reshaping die 32 which is suitable for producing asimple offset is shown in FIG. 3. The reshaping die 32 is comprised of alower die part 54 and an upper die part 56 which can be separated fromeach other by a predetermined distance sufficient to permit compositeproduct 27 emerging from pultrusion die 26 to freely pass therebetween,and which can be brought together and urged upon uncured portions ofproduct 27 to reshape the same. The die parts 54 and 56 can be broughttogether to reshape portions of the pultruded product 27 or retracted byany of various means such as pneumatic or hydraulic cylinder means 57 towhich a hydraulic or pneumatic fluid is supplied. Alternate means suchas mechanical jack screws or scissors mechanisms can be employed. Thereshaping die 32 includes heating means such as electrical resistancestrip heaters 58 and cooling means such as cooling coils 62(schematically illustrated in FIG. 3) Any of various alternativeconventional heating and cooling means known to the art may be providedto heat the reshaping die to a temperature which is sufficient to effectcuring of the thermosetting resin of an uncured portion of pultrudedproduct 27 emerging from pultrusion die 26 and thereafter cool thereshaping die to a temperature below that which will cause significantcuring. It is preferable that the reshaping die include cooling means inorder to avoid surface precure when the uncured portion is drawn betweenthe open reshaping mold parts.

The process of the present invention differs from conventionalpultrusion processes by operating under non-steady-state conditions sothat selected portions of the composite product 27 emerging from thepultrusion die are substantially uncured, while other portions,generally the majority of the composite 27, are substantially fullycured. The expression "substantially uncured portion" as used hereinrefers to a portion of material which has emerged from the pultrusiondie and which can be reshaped such as by pressure molding and cured toform a rigid solid which cannot be again reshaped by pressure molding.To retard or prevent cure during the cooling cycle, preferably the dietemperature is lowered to below the initiation temperature of the resin,i.e. to the temperature which results in less than 5% reaction but morepreferably less than 3% and even no reaction proceeding during theadvance of the uncured material through the cooled die to the reshapingdie.

The expression "substantially fully cured portion" as used herein refersto a portion of material which has emerged from the pultrusion die whichhas cured sufficiently such that it is a rigid solid which cannot bereshaped by pressure molding. Typically, these portions will have atleast about 80%, preferably 90% and most preferably 95% by weight ofpolymers and reacted monomers in the form of a cross-linked thermoset.

To affect cure of the thermosetting material, preferably the pultrusiondie 26 has a ramped or zoned temperature profile which can beexemplified for peroxide initiated polyester or vinyl ester resins ashaving an entrance temperature maintained at about 20° F. below thereaction initiation temperature, an increasing temperature ramp zoneextending over about 18 inches with a maximum temperature of about 300°F. to 375° F., and an optional decreasing temperature zone comprisingthe remaining die length wherein the minimum temperature of the zone isdetermined by the appearance or integrity of the cured composite. Inpractice the die exit temperature is within about 50° F. to 100° F. ofthe die maximum temperature. For epoxy resins, a generally hotter dieprofile is utilized with an entrance temperature of 200° F. and a diemaximum temperature of 400° F. to 450° F. With all of the subjectresins, the extent of reaction (or cure) will depend on the temperatureas well as the residence time in the die. For example, a certain thermalprofile of a die may achieve 95% reaction at one speed and only 80%reaction at a faster line speed (yielding higher production speed butlowered physical properties).

During start up, the reinforcing fibers can be drawn by hand throughguide 14, resin bath 16, forming guides 22, pultrusion die 26 and freelybetween spaced die parts 54 and 56 of reshaping die 32 togripping/pulling means 28. After the temperature within at least aportion of the pultrusion die 26 is raised to a temperature sufficientto effect curing of the heat curable thermosetting resin composition,the material 27 is engaged by the gripping/pulling means 28 which can beany conventional means known for continuously drawing pultruded materialthrough a pultrusion die. The gripping/pulling means must generally beregulated to avoid damage to any reshaped portion having a cross-sectionwhich is different from that of material emerging from the pultrusiondie 26. Specifically, means should be provided to sense any reshapedportions and avoid engagement of the gripping/pulling means with thereshaped portions to prevent damage to the pultruded product.Particularly preferred gripping/pulling means include conventionalreciprocating clamp type pullers 80, as shown in FIGS. 4 and 4a, whichare used in association with means for sensing and avoiding clampingonto the reshaped portions of the pultruded products.

The reciprocating clamp type puller 80 includes a lower gripper 82 whichis stationary relative to the frame of the puller 80, and an uppergripper 84 which is vertically movable between an unclamped position(shown in phantom) and a clamped position (shown in solid lines).Alternatively, a stationary upper clamp and movable lower clamp designmay be employed. When the upper gripper 84 is in the clamped positionthe pultruded product is firmly held or gripped between the upper andlower grippers. The entire reciprocating clamp type puller 80 is movablein the machine direction (indicated by arrow 86) to pull the pultrudedmaterial through the pultrusion apparatus when the upper gripper is inthe clamped position. A similar or identical reciprocatinggripper/puller mechanism is preferably situated directly after the firstgripper/puller means such that with alternating cycles the product beingpulled through the pultrusion die experiences an essentially continuousmotion. After the puller 80 has pulled material 27 a predetermineddistance through the apparatus, such as from position A to position B(as shown in FIG. 4), gripper 84 is raised to the unclamped position andpuller 80 is moved backwards in a direction opposite to the machinedirection (as indicated by arrow 88 in FIG. 4a) to a position C wherethe gripper 84 can be lowered back into the clamped position to pullmore material 27 in the machine direction. The puller 80 is preferablyused in association with a detector means 90 which includes a rotatablelever 92 and a follower wheel 94 which rolls along the surface of thematerial 27 as it is being pulled through the pultrusion apparatus. Whena portion of the material 27 having a reshaped portion, such as anoffset 96, passes by the wheel 94, lever 92 rotates slightly activatinga switch in detector means 90 to record the position of the offset 96 sothat puller 80 is instructed to avoid clamping onto that position.Alternatively, any non-contact sensing device including but not limitedto ultrasonic, capacitive, or photoelectric means may be utilized tosense and define the position of cross-sectional changes to be avoidedby the clamping device. A predetermined length of cured compositematerial 27 can be pulled from pultrusion die 26, at a line speed offrom about 1 to about 180 inches per minute, or more typically fromabout 12 to about 72 inches per minute.

After the desired length of substantially fully cured composite has beenprepared, the temperature in the pultrusion die 26 is rapidly reduced,such as by exposing the outer surfaces of the pultrusion die to acooling fluid (liquid or gas) under turbulent flow conditions to provideadequate convective heat transfer, to cool the inner die surfaces 38 and40 to a temperature at which curing of the thermosetting resin does notoccur at an appreciable rate. It is generally desirable to draw material22 into the pultrusion die at a very slow rate, or more preferablydiscontinue pulling material into the die 26 while it is being cooled inorder to provide a sharp transition between the cured and uncuredportions of the material 27 emerging from the die 26. It is generallypossible to achieve a transition from substantially fully cured tosubstantially uncured material which is less than 1 or 2 inches. Afterthe die 26 is cooled to a temperature which is sufficiently low toprevent any significant curing of the thermosetting material residingtherein, a predetermined length of substantially uncured composite ispulled through the die 26. After the desired length of substantiallyuncured material has been drawn from the die 26, the die is reheated toa temperature which will cause the thermosetting material entering thedie 26 to cure. This process of periodic cooling of the pultrusion die,drawing of uncured material from the die 26, reheating of the pultrusiondie, and drawing of cured material from die 26 can be repeated asdesired to produce a plurality of pultruded products having curedportions and uncured portions. Cutting means 30 are used to cut thepultruded composite 27 into individual articles.

The process and apparatus of the invention generally allows any desiredlength of substantially fully cured material to be drawn from thepultrusion die followed by generally any desired length of substantiallyuncured material which can be reshaped and cured to form variousfiber-reinforced thermoset articles having variable cross-sectionalgeometries. The material exiting the pultrusion die can generally haveany combination of uncured linear segments and cured linear segments.The apparatus can be manually controlled, but it is generally preferablethat the apparatus be computer controlled, especially when the length ofthe cured and/or uncured portions of material leaving the pultrusion die26 is to be varied from one product to the next.

The uncured portions of the composite 27 emerging from pultrusion die 26are preferably reshaped in-line immediately downstream of the pultrusiondie by means of a compression or reshaping die 32 having heating means58 to allow for in-line reshaping and curing of the uncured portions ofcomposite 27. The reshaping die 32 is preferably positioned immediatelyadjacent to the pultrusion die so that the uncured portion of materialemerging from die 26 can be reshaped and cured before significantamounts of monomers or other volatile materials in the thermosettingresin composition evaporate. The reshaping die 32 can be eitherstationary or movable along a linear path generally in line with theaxial or machine direction of the pultrusion die, in which case thereshaping die 32 can also serve as an auxiliary gripping/pulling device.Alternatively, the uncured portions of the composite 27 emerging frompultrusion die 26 can be reshaped at a separate molding station afterbeing cut into individual articles. The reshaping die 32 may incorporatea provision to pierce and/or selectively shear fibers during the closureof the die which allows local reshaping beyond the normal elongationlimits of the reinforcing fibers. Such a feature would allow forintegrally molded holes and tabs normally requiring secondaryfabrication steps. For example, upper die part 56 can be provided with apiercing protrusion 98 (as shown in FIG. 5) which cuts through material27 when die parts 54 and 56 are drawn together (as shown in FIG. 5a) toreshape a portion of material 27. Die part 54 is provided with a recesswhich generally conforms to the piercing protrusion 98 and cooperatestherewith to form a projecting tab 100 (shown in FIGS. 6 and 6a) andslot 102.

The present invention has been illustrated by reference to a simpleexample wherein a sheet or strip is provided with an off-set, however itshould be understood that the die 32 can be configured to provide avariety of different shapes such as transverse ribs, transverse flanges,transverse bosses or protrusions, and the like. Resin, fibers, insertsand or other materials can be added to the uncured portions of materialexiting curing die 26 and integrally bonded thereto during the reshapingand curing steps. The ribs, flanges, bosses and the like can be utilizedto facilitate better mechanical joints which provide for more effectivetransfer of mechanical loads from the pultruded article to anotherstructure. For example, the off-set sheet or strip bar product which isillustrated above can be used to provide a superior lap joint whereinlongitudinal compressive loads can be transferred from one pultrudedmember to another. Another example wherein the invention can beeffectively utilized is in the fabrication of C-channel troughs. Inaccordance with the method of the invention, such C-channel troughs canbe provided at one end with an off-set channel designed to receive theunmodified end of a similar C-channel trough providing an overlap buttjoint which need only be sealed at one end, thereby reducing the laborneeded to join trough members together. Another example is thetermination of oil well sucker rods. Current rod terminations utilizemetal fittings which are adhesively bonded to a constant cross-sectionrod in a manner which promotes rod tensile failures rather thaninterface failures. This approach requires a fairly massive fittingwhich adds to the sucker rod string weight. As an alternative, themethod of the invention can be used to provide a modified geometry atthe end of the rod which allows a mechanical support which fullyutilizes the tensile load of the rod without the risk of damaging thecomposite structure. For example, the process of the invention can beused to make an oil well sucker rod with an end portion whichtransitions from a circular to an oval cross-section (as shown in FIG.7) which allows use of the geometric change to mechanically transferload from a fitting to the rod without relying entirely upon an adhesiveinterface.

The invention is also useful for preparing tubular products (such asshown in FIG. 8) having a reshaped reduced outer cross-sectionalperimeter at one end which conforms to the inner perimeter of theremaining portions of the tubular product which emerged from thepultrusion die fully cured. Such products can be joined together moreeasily by inserting the reshaped end of one tube to the unmodified endof a similar product, and will facilitate better load transfer andjoining without the need for internal connecting plugs or externalsleeves. In a similar manner, tubular reducing tapers (such as shown inFIG. 9) may be introduced at the end of a substantial length of constantcross-section profile. Virtually any cross-sectional transformation canbe accommodated by proper design of the reshaping means withconsideration for the limits of fiberous material displacement. Forexample, the process and apparatus of the invention can be used toproduce pultruded products having a shape transformation such as from arectangular tube to a I-shape cross-section (as shown in FIG. 10).

Generally, any of the various known heat curable thermosetting polymericresin compositions such as those based upon unsaturated polyesters,vinyl esters and epoxies can be utilized with the invention. Othersuitable resins include heat curable thermosetting methacrylate resins,modified phenolic resins, bismaleimide resins, and the like. Inparticular the process and apparatus is not limited to additionpolymerization thermosetting compositions, but instead may employgenerally any known thermosetting composition. Such compositions caninclude conventional amounts of reactive prepolymers, oligomers, ormonomers; fillers; pigments; mold release agents; flame retardants; lowprofile agents; catalysts; inhibitors; air release agents; impactmodifiers; and the like. Such heat curable thermosetting resincompositions are well known to the art of plastic molding and moreparticularly to the art of pultrusion.

As used herein, "reinforcing fibers" includes filaments, yarn, roving,mats, felt, ribbon, tape, fabric and the like in continuous form,usually aligned parallel to the flow of material and including stitchedor braided fibers. Any combination of continuous reinforcements cangenerally be used. The number and arrangement of the fibers used in theprocess of the invention will vary according to the particularcross-sectional shape of the article being formed and can readily bedetermined by a person skilled in the art of pultrusion. Usually, thefiber content of the pultruded product 27 is from about 25 to about 80weight percent based on the total weight of the composite material.

The fiberous reinforcing material can be any conventional materialsuitable for reinforcing means, including metal fibers, glass fibers,carbon fibers (graphite), boron fibers, ceramic fibers, Kevlar® fibers,synthetic organic fibers such as polyamide and polyethylene fibers, andvarious other inorganic or organic fiberous materials known to be usefulfor reinforcing thermosetting polymeric compositions, such as cellulose,asbestos, cotton and the like.

While the invention has been described with reference to the preferredembodiment wherein dry reinforcing fibers are directed through a resinbath and impregnated with the heat curable thermosetting resincomposition contained within the bath, it should be understood thatpreimpregnated reinforcing fibers (i.e. prepreg tapes and the like) canbe utilized with the invention. In such case, the heat curablethermosetting resin preimpregnated reinforcing fiber material isgenerally refrigerated prior to use. Where preimpregnated reinforcingfibers are used, such preimpregnated reinforcing fibers are drawndirectly into the forming die 22, and the guide 14 and resin bath 16 canbe eliminated from the process.

While in accordance with the patent statutes the best mode and preferredembodiment has been set forth, the scope of the invention is not limitedthereto, but rather by the scope of the attached claims.

What is claimed is:
 1. An apparatus for preparing a fiber-reinforcedthermoset article, comprising:an elongate die having a die cavity abouta longitudinal axis therethrough; means for selectively pulling at leastat a first rate of speed and a second rate of speed a continuousmaterial comprised of reinforcing fibers which are impregnated with aheat curable thermosetting resin composition through said die, saidsecond rate of speed being very slow or stopped; activatable means forheating at least a portion of the entire length of said die to atemperature which is sufficiently high to cause said heat curablethermosetting resin composition in said die to cure, said heating meansbeing activatable to heat said die to transfer heat said material whenit is pulled at said first rate of speed through said die; andactivatable means for cooling at least said portion of said die to atemperature which is sufficiently low to prevent said heat curablethermosetting resin composition in said die from curing so that whensaid continuous material is pulled at said second rate of speed saidcooling means is activatable to prevent said die from heating saidcontinuous material to a cure temperature and means for reshaping andcuring uncured material which has been pulled from said die.
 2. Theapparatus of claim 1, wherein said means for reshaping and curing is apressure molding apparatus having conforming mold parts, and includingmeans for heating said conforming mold parts to a temperature which issufficiently high to cause said thermosetting resin composition to cure.3. The apparatus of claim 2, wherein said pressure molding apparatusincludes means for cooling said mold parts to a temperature which issufficiently low to prevent said thermosetting resin composition fromcuring.
 4. The apparatus of claim 3, wherein the pressure moldingapparatus is movable along a linear path generally in line with thedirection of the longitudinal axis of the die cavity, said pressuremolding apparatus acting as an auxiliary gripping/pulling device.
 5. Theapparatus of claim 2, wherein said pressure molding apparatus includesmeans for piercing or shearing fibers of said continuous material. 6.The apparatus of claim 1, wherein said die has an outer wall and aninner wall which define said die cavity and the maximum distance fromany point on the die inner wall to a point on the outer wall of said dieis less than about 1/2 inch.
 7. The apparatus of claim 1, wherein saidpulling means comprises reciprocating clamp puller means including meansfor sensing and avoiding clamping onto any portion of pultruded materialwhich has been reshaped.
 8. The apparatus of claim 1, wherein said diecomprises;a plurality of die parts which can be securely assembled intoan elongate die defining a die cavity, a wall thickness of said diebeing the perpendicular distance from a point on the die cavity wall toa point on the outer wall of said die, said thickness of said die at anypoint on the die cavity wall being less than about 1/2 inch.
 9. Anapparatus as set forth in claim 1, wherein said die comprises a seamlesselongate tubular die having an outer wall and an inner wall whichdefines a die cavity, a wall thickness of said seamless die being theperpendicular distance from a point on the die inner wall to an opposingpoint on the outer wall of said die, the thickness of said die at anypoint on the die cavity wall being less than or about 1/2 inch.
 10. Anapparatus as set forth in claim 1, wherein said die has a wall thicknessso as to yield a deformation of no more than 0.002 inch when subjectedto an internal outwardly acting pressure of 200 psi.
 11. An apparatusfor preparing a fiber-reinforced thermoset article, comprising:anelongate die having a die cavity about a longitudinal axis therethrough;means for pulling a continuous material comprised of reinforcing fiberswhich are impregnated with a heat curable thermosetting resincomposition through said die; means for heating at least a portion ofthe entire length of said die to a temperature which is sufficientlyhigh to cause said heat curable thermosetting resin composition in saiddie to cure; means for cooling at least said portion of said die to atemperature which is sufficiently low to prevent said heat curablethermosetting resin composition in said die from curing; means forreshaping and curing uncured material which has been pulled from saiddie; said pulling means comprises reciprocating clamp puller meansincluding means for sensing and avoiding clamping onto any portion ofpultruded material which has been reshaped.
 12. An apparatus as setforth in claim 11, wherein said die has a wall thickness which isgenerally conforming to the cross-sectional shape of the die cavity. 13.An apparatus as set forth in claim 11 which includes computer means forcontrolling the means for pulling, the means for heating and the meansfor cooling.
 14. An apparatus for preparing a fiber-reinforced thermosetarticle, comprising:an elongate die having a die cavity about alongitudinal axis therethrough; a puller for selectively pulling atleast at a first rate of speed and a second rate of speed a continuousmaterial comprised of reinforcing fibers which are impregnated with aheat curable thermosetting resin composition through said die, saidsecond rate of speed being very slow or stopped; a heater for heating atleast a portion of the entire length of said die to a temperature whichis sufficiently high to cause said the curable thermosetting resincomposition in said die to cure, said heater being activatable to heatsaid die to transfer heat to said material when it is pulled at saidfirst rate of speed through said die; and a cooling jacket for coolingat least said portion of said die to a temperature which is sufficientlylow to prevent said heat curable thermosetting resin composition in saiddie from curing so that when said continuous material is pulled at saidsecond rate of speed, said cooling jacket is activatable to prevent saiddie from heating said continuous material to a cure temperature; acomputer for controlling the puller, the heater and the cooling jacket;and a pressure molding apparatus for reshaping and curing uncuredmaterial which has been pulled from said die, said pressure moldingapparatus having conforming mold parts, and including a heater forheating said conforming mold parts to a temperature which issufficiently high to cause said thermosetting resin composition to cure.